Glucosamine, one of the world's best-selling joint supplements with over 40 million Americans taking it each year, just got an unwelcome spotlight. A University of Florida study published June 9 in *Nature Metabolism* found that people with mild cognitive impairment who took glucosamine had a 25% higher likelihood of progressing to full Alzheimer's disease — and diagnosed patients faced a 25% higher risk of death within five years.
The team used AI to comb through anonymized University of Florida Health records from 2012 to 2024: more than 24,000 patients with dementia (including Alzheimer's) and nearly 42,000 with mild cognitive impairment, about 8% of whom had documented glucosamine use. After adjusting for age, sex, and other factors, glucosamine users with mild cognitive impairment were 25% more likely to progress to dementia — a notable jump against a typical progression risk of around 5%.
Why would a joint supplement implicate the brain? Glucosamine is a sugar-related molecule that can cross the blood-brain barrier. The researchers found elevated protein glycosylation — the process of attaching sugar molecules to proteins — in brain tissue from Alzheimer's patients compared with healthy brains. Glycosylation is essential for normal cell function, but it appears to run overactive in the Alzheimer's brain.
Mouse experiments back it up: feeding glucosamine to Alzheimer's-model mice worsened memory deficits, while pharmacologically blocking the glycosylation pathway improved memory. Healthy mice given the supplement showed no effect.
Lead researcher Matt Gentry, chair of biochemistry and molecular biology at the University of Florida, stressed: "While it's an association and not proof of causality, it does raise an important clinical question that now deserves much more attention." The team hypothesizes that the Alzheimer's brain, with its pre-existing metabolic changes, responds differently to glucosamine than a healthy brain.
Two groups should take note: older adults with mild cognitive impairment — the exact demographic most likely to take glucosamine — and diagnosed dementia patients still on the supplement. The researchers suggest these patients discuss continued use with their doctors, and that clinicians add glucosamine use to their intake checklists.
Caveats apply to the alarm, too: the study rests on retrospective medical records and animal experiments, not randomized controlled trials — the causal chain isn't nailed down. The team's next step is to dissect the glycosylation mechanism further, laying groundwork for future intervention trials. For consumers, the takeaway is simple: don't play doctor — ask one.